1. Field of the Invention
The present invention relates in general to navigational instruments and more specifically to sextants and other instruments used in celestial navigation.
2. Prior Art
Celestial navigation depends on the ability to obtain a precise measurement of the altitude of a celestial body above the viewer's horizon at a precise moment in time. From this datum, called the sextant altitude, the navigator's line of position (LOP) may be calculated. To perform this calculation it is necessary to algebraically subtract the sextant altitude from the calculated altitude of the body, which may be obtained by applying formulae from the Almanac for Computers or by computing them from tables. From two or more observations of different celestial bodies, the point at which two or more LOP's cross is the fix, or position. In the past, the sextant used to determine the altitude of the celestial bodies has usually been a handheld device consisting of a telescope, a mechanical arm, two mirrors, and a rigid arc. In normal usage, the navigator sights the horizon through the telescope and simultaneously sights the celestial body by means of the mirrors, adjusting a movable arm along the arc until the celestial body appears to align with the horizon, and then noting the angle as indicated by the graduation marks on the arc.
Improvements to the basic sextant are known, which increase its precision, automate the timing of an observation, read the angle electronically, combine with a computer to plot position, or average a number of individual observations to improve accuracy and precision. However, there is no known device which comprises an electronic artificial horizon, an automatic segmented diode device for sighting and identifying the celestial body, plus microchips and software that are capable of averaging multiple observations and plotting a fix; nor is there any known electronic device which controls precision of individual altitude measurements by switching power off and on depending on how closely the instrument is trained on the target celestial body; nor is there any known device which performs navigational functions by averaging the direction of radio waves from artificial satellites for which the ephemerides are known.
There is known to be a device called an Electronic Sextant (Laxo, U.S. Pat. No. 4,197,653), but this device requires the navigator to take a conventional sextant reading, in which a mechanical arm is moved along an arc.
There is also known to be a device termed a Passive Optical Rangefinder-sextant (Barton, U.S. Pat. No. 4,162,124), but such device has neither an electronic artificial horizon nor an averaging capability.
There is also known to be an Automatic Space Sextant (Owen, U.S. Pat. No. 4,082,462), but such device requires two telescopes and uses generated time pulses from a momentum wheel to provide an angle between the two bodies. This device is designed solely for space use and has neither an electronic artificial horizon nor accompanying software to statistically enhance readings and to display the fix.
There is also known to be a Horizon Indicating Device for Marine Sextant (Ho Shiaw-Lei, U.S. Pat. No. 4,005,938), but this device provides a mechanical horizon finding device, not an electronic artificial horizon.
There is also known to be an Electronic Sextant (Leuchter, U.S. Pat. Nos. 3,968,570) and an Automatic Sextant (Decker, 4,763,418 and Decker, 4,707,926), which does not provide an electronic, artificial horizon nor statistically enhance numerous individual observations--taken either automatically or in a handheld mode--nor provides position information on a video display terminal.
There is also known to be a Sextant Having a Microprocessor for Calculating the Position of Heavenly Bodies (Sigley, U.S. Pat. No. 4,702,011), but such device uses a conventional prior art sextant without an artificial electronic horizon. Such device also differs from the present invention in that it cannot be operated in a fully automated mode.
There is also known to be an Optical Device for Vertically Positioning a Sextant (Davies, U.S. Pat. No. 4,428,671), but said device is designed solely to minimize tilt error which the present device accomplishes, when necessary, by provision of a second inclinometer mounted cross-axis to the first inclinometer.
In addition, there are known to be inventions which determine a vehicle's position based on radio frequency signals, or in which a visual display of the heading and position is provided on a terminal (Schneiderhan et al., 4454583), but there is no known device that provides heading, position and other navigational information on a display terminal when the information is derived from celestial navigation or by averaging numerous individual observations (of light or radio wave signals).
There are also known to be inventions (Haefner, German Patent Document No. 3122901) which digitize map information for navigational purposes, or which solve (Cadoux, British Patent Document No. 2101060) navigational problems, but there are no known devices which perform these tasks in conjunction with data that derives from celestial objects or which has been statistically enhanced from numerous individual observations.
There are also known to be devices for providing map information for a moving land vehicle (Hasebe, U.S. Pat. No. 4,470,119), but there are no known devices which provide such information deriving from continuous position fixes from celestial objects or from radio frequency sources.
There is also known to be a device for calibrating an aircraft's heading system by reference to a celestial body (Wright, U.S. Pat. No. 3,245,147), but said device is of a mechanical nature and does not provide the automated features of the ARS.
No device is known for combining in a single instrument an electronic means of providing an automatic angle reading capability by use of an electronic inclinometer plus an electronic averaging method combining a microchip and software. In addition, there is no known device for completely automating the sextant by providing for a fixed position sextant which combines an electronic artificial horizon, soft ware that recognizes celestial bodies and measures their altitude, as well as performing sight reduction functions and displaying results on a video display terminal. Nor is there known any type of sextant which is self calibrating, or that is combined with software to statistically improve numerous individual altitude readings. Nor is there any known sextant which combines with software to read a vehicle's or a craft's instruments, thereby providing the capability of displaying position, course, speed and attitude information on a video display terminal.